1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a liquid crystal display and a pre-charging method thereof wherein data lines can be pre-charged to simplify a circuit configuration.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls light transmittance of a liquid crystal in accordance with a video signal to thereby display a picture. The LCD includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix type, and a driving circuit for driving the liquid crystal display panel. The liquid crystal display panel includes a plurality of thin film transistors as switching devices for making an active driving of each liquid crystal cell.
The thin film transistor is classified into an amorphous thin film transistor using amorphous silicon and a polycrystalline thin film transistor using polycrystalline silicon. Herein, the polycrystalline thin film transistor employs polycrystalline silicon having about hundred times faster electric charge mobility than amorphous silicon such that the driving circuit can be built in the liquid crystal display panel.
As shown in FIG. 1, a liquid crystal display panel 18 employing such polycrystalline thin film transistors includes a pixel matrix 16 for displaying a picture, and a plurality of demultiplexers 14 for making a time division of data lines DL of the pixel matrix 16 to supply video signals from an external data driving integrated circuit (D-IC) 10 thereto. Further, the liquid crystal display panel 18 includes a static electricity proof (electro-static discharge ESD) circuit 12 connected to a plurality of video lines VL supplied with video signals from the data D-IC 10 to prevent static electricity.
The pixel matrix 16 includes a liquid crystal cell and a thin film transistor for independently driving the liquid crystal cell for each area defined by the gate lines GL and the data lines DL. The gate lines GL are sequentially driven by a gate D-IC (not shown). The data lines DL charge video signals supplied, via the demultiplexers 14, from the data D-IC 10 every horizontal period when the gate lines GL are driven. The liquid crystal cell reacts a liquid crystal having a dielectric anisotropy by the charged video signals to control light transmittance, thereby implementing a gray level scale. The liquid crystal cell consists of a pixel electrode connected to the corresponding thin film transistor, and a common electrode opposed to the pixel electrode with the liquid crystal therebetween to supply a reference voltage, that is, a common voltage Vcom.
The plurality of demultiplexers 14 divide the data lines DL into a plurality of blocks for their driving. For instance, each of the demultiplexers 14 makes a time-divisional driving of each three data lines DL. Each of the demultiplexers 14 includes first to third sampling switches SW1 to SW3 for sequentially applying video signals supplied, via the video lines VL, from the data D-IC 10 to three data lines DL in response to first to third control signals MUX1 to MUX3 inputted from the exterior thereof.
More specifically, the first to third sampling switches SW1 to SW3 of the demultiplexer 14 are sequentially driven with the first to third control signals MUX1 to MUX3 in a video signal charge interval T2 of a time interval when one gate line GL is turned on as shown in FIG. 2, and applies video signals inputted via the video lines VL to the corresponding data lines DL. Further, the first to third sampling switches SW1 to SW3 of the demultiplexer 14 are turned on at the same time in response to a pre-charge control signal PS included in the first to third control signals MUX1 to MUX3 in a pre-charge interval T1 prior to the charge interval T2 of the video signals of the turn-on interval of the gate line GL. The turned-on first to third sampling switches SW1 to SW3 pre-charge the data lines DL by a pre-charge voltage supplied, via the video lines VL, from the data D-IC 10. The pre-charged data lines DL rapidly charge video signals supplied in the charge interval T2, thereby shortening a charge time of the video signals.
The ESD circuit 12 includes first and second diodes D1 and D2 connected, in series, between the first and second power lines PL1 and PL2. A node between the first and second diodes D1 and D2 is connected to the video line VL. Herein, the first and second diodes D1 and D2 consist of a plurality of thin film transistors. More specifically, when a voltage higher than a first supply voltage Vposi is inputted via the video line VL due to static electricity, the first diode D1 is turned on to thereby discharge the inputted voltage into the first power line PL1. On the other hand, when a voltage lower than a second supply voltage Vnega is inputted due to static electricity, the second diode D2 is turned on to thereby discharge the inputted voltage into the second power line PL2. Thus, it becomes possible to prevent the static electricity from being flown, via the video lines VL, within the liquid crystal display panel 18. Further, when video signals having a value between the first and second supply voltages Vposi and Vnega are supplied via the video lines DL, the first and second diodes D1 and D2 of the ESD circuit 12 are turned off to make no impact on the video signals. For instance, 10V/−8V or 10V/0V is used as the first and second supply voltages Vposi and Vnega, and a voltage in the range of 1V to 9V is applied as a video signal via the video lines VL.
The conventional polycrystalline-type LCD having the above-mentioned structure pre-charges the data lines DL using a pre-charge voltage supplied from the data D-IC 10 mounted onto the exterior side of the liquid crystal display panel 18. In this case, a design of the data D-IC 10 under consideration of the pre-charging becomes complicated. Furthermore, a strategy of configuring a separate pre-charge circuit within the liquid crystal display panel has been suggested, but it brings about a complicated circuit configuration of the liquid crystal display panel.